Constant leakage system for hydraulic apparatus



y 1938- r R. w. DlNZL 2,117,303

CONSTANT LEAKAGE SYSTEM FOR HYDRAULIC APPARATUS Filed Dec. 23, 1935INVENTOR Patented May 17, less uurrsn STATES PATENT OFFICE o'onsras'r'LEAKAGE srsrmr roa msauuoarrm'rus tion of Delaware Application December28, 1983, Serial No. 703,862

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This invention relates generally to an improved hydraulic system andmore particularly to an improved combination of a materials testingmachine oi the ram type and means for maintain- 3 ing constant leakagein the hydraulic system thereof whereby for varying loads asubstantially constant speed of loading may be eii'ected.

A constant speed or rate of -loading on a test specimen is highlydesirable but this is rendered b diilicult in ram type machines because01' leakage around the ram or in the other parts oi the system.

Ahydraulic rain in a materials testing machine cannot be made leakproofit it is desired to main- 15 tain maximum accuracy and sensitivity, andthis factor taken with the tact thatramleakage varies. with the loadthereon, presents a complex problem. While constant speed systems .haveheretofore been proposed, yet they make no at- 2 tempt to utilize theprinciple of a constant leakage system as herein disclosed, but on thecontrary employ the principle oi a variable leakage system.

It is an object of my invention to provide a hydraulic ram system havingsubstantially constant leakage for varying loads.

A further object of the invention is to provide an auxiliary, leakagevalve mechanism in com- I bination with a source oi fluid pressure andram '0 type apparatus so that the valve mechanism permits a variableartificial leakage to compensate for variable ram leakage or othersources of leakage in the system as a whole, whereby for light loads andsmall ram leakage a high rate oi artificial leakage occurs and viceversa for large loads and corresponding high ram leakage, thusmaintaining constant leakage in the system.

Another object is to provide a pressure actu ated valve mechanismfunctioning automatically to vary the artificial leakage in accordancewith the ram pressure.

Other objects and advantages will be more apparent to thoseskilled inthe art from the following description of the accompanying drawing 5 inwhich:

Fig. 1 is a vertical section through one form of ram type materialstesting apparatus showing diagrammatically the application of myconstant leakage system; v

Fig. 2 is an enlarged vertical section through the valve mechanism foreffecting the constant leakage.

In the particular embodiment of the invention which is disclosed hereinmerely for the purpose a of illustrating one specific i'orm amongpossible others that the invention might take, I have shown generally aram type testing machine such as disclosed in the application of G. 8.von Heydekampi, Serial No. 666,315, filed April 15, 1933, although itwill of course be understood 5 that various other forms of ram typemachines may be employed. This machine is provided with lower and upperstationary platens I and I held in fixed spaced relation by a series ofjoining columns 3. A lower or intermediate movable platen l is securedby a series 0! rods 5 to an upper crosshead 6. The hydraulic ramincludes a cylinder 1 supported by the upper stationary platen I, thecylinder being specifically shown as of the rotatable sleeve typealthough this could be nonrotatably secured to platen 1 as in certaintypes of ram machines. The rotatable feature of sleeve l is merely forthe purpose of reducing friction of rest as outlined in said VonHeydekampi application. Reciprocably disposed within cylinder I m is aram 8 resting against crosshead l.

Hydraulic pressure may be supplied irom a sump 9, thence through amotor-driven pump ll of any suitable form such as gear pump or positivedisplacement pump. The fluid is passed a through pipe II and es II inplaten 2 tothe interior of cylinder 1, thereby to move ram 8 upwardly.As the ram moves upwardly, crosshead I and rods 5 will likewise pullplaten 4 upwardly to impose a test load on a specimen ll which is heldby suitable grips in base i and platen 4. In the event of a compressiontest in distinction to the tension test illustrated in Fig. 1, aspecimen is interposed between platens 2 and 4, thereby allowinghydraulic pressure to load the specimen in the same manner as for atension test.

It is desirable to maintain a constant rate or speed of loading of thespecimen and to thisextent it is necessary to compensate for leakagebetween the ram I and its cylinder 1 and any other sources of leakage inthe system. To do this I have disclosed herein the principle oi aconstant leakage system whereby the ram or other leakage is supplementedbyan artificial leakage, the sum of the two leakages remaining constantfor varying load pressures. This artificial leakage is effected by theprovision of an improved combination 01' elements including a bypassgenerally indicated at I! controlled by a valve I U. This valve 5 has abore l1 and a piston ll normally urged downwardly by a spring ll. At itslower or maximum leakage position the piston engages an ad- Justablestop stud 2i. Fluid pressure from the ram or pump side is admittedbeneath piston I I as through a pipe 2 i, this fluid flowing through aseries of preferably inclined passages 22 to a central passage ororifice 23 from which it flows outwardly through a pipe 24 to return tosump 9. To automatically vary the artificial leakage through piston i 8,there is provided a needle valve 25 having a point of curvaturedetermined in accordance with varying loads and ram leakagecharacteristics. At low pressure, and therefore minimum ram leakage,piston I8 is in the positlon shown in Fig. 2 thereby permitting maximumartificial leakage, whereas when the load pressure increases and leakagepast ram 8 also increases, the increased fluid pressure will move pistonl8 upwardly against the action of spring I! so that the curvature '26 ofneedle 25 will reduce the outlet area of orifice 23 and restrict theartificial leakage to maintain a constant total leakage in the system.While the artificial leakage is thereby varied, the ram leakage variesalso but the sum of the two leakages remains constant throughoutvariations in load due to the particular shape 26 of needle valve 25.Hence it is seen that so long as fluid pressure is supplied at aconstant rate the ram 8 will move at a constant speed irrespective ofthe load. The shape of the needle valve or its cooperating orifice willof course be different for ramsof diflerent leakage characteristics,this being determined experimentally.

From the ioregoing disclosure it is seen that I have provided anextremely simple and efi'ective means for overcoming the problem ofleakage and I am able to do this without auxiliary apparatus forincreasing either the speed or discharge ofthe pump to make up for avarying leakage; and it is also seen that my improved constant leakagesystem is applicable whether the load is increasing or decreasing as thespring i! will cause downward movement of piston II to increase theartificial leakage when the load decreases.

It will of course be understood that various changes in details ofconstruction and arrangement 01' parts may be made by those skilled inthe art without departing from the spirit of the invention as set forthin the appended claim.

I claim:

A constant speed mechanism for a hydraulic loading system comprising, incombination. a main pipe through which fluid is supplied to the system.a valve mechanism having a casing and a piston therein, a passage forbypassing fluid out of said pipe to one end of said casing beneath saidpiston, a free atmospheric outlet communicating with the other end ofsaid casing above said piston whereby the top 01 the piston is subjectedto atmospheric pressure, means on the top of said piston formechanically biasing the same against-the pressure acting on the bottom01' the piston, an orifice for allowing flow of pressure fluid from theunder side of the piston to the top atmospheric side thereof, and meansresponsive to movement of said piston caused by progressive increases ofpressure in said main pipe for automatically progressively restrictingsaid orifice so as to maintain a substantially constant rate of flowthrough said pipe.

RICHARD W. DINZL.

